Thermochemical equilibrium calculations of high-temperature O2 generation on the early Earth: Giant asteroid impacts on land

Earth s atmosphere is composed primarily of N2 and O2. The origin of free O2 in the early Earth s atmosphere is still subject of considerable debate.1 Theoretical models suggest that the initial form of free O2 in the atmosphere has been oceanic H2O. Recent computation modelling has suggested that a superheated (ca. 2000 K) H2O vapor atmosphere of 1.4x1021 kg (the present mass of the oceans) lasting for about 3000 y could probably have been formed on Earth by an enormous (ca. 1028 J) asteroid impact. In this report, the occurrence of the thermochemical dissociation of the vapor, creating a primitive oxygenic (ca. 0.1 of the present level (PAL) of free O2) atmosphere.